Compressed natural gas (CNG) is a high octane fuel that is beneficial for reducing engine knock, for reducing hydrocarbon emissions in cold start events, and for reducing carbon dioxide emissions during engine operations. However, CNG has a low energy density compared to liquid hydrocarbon fuels, such as diesel fuel or gasoline. To increase the range and total fuel quantity stored in a vehicle, CNG may be utilized in conjunction with gasoline or diesel fuel, requiring the vehicle to switch between fuels for optimal performance. However, inclusion of separate fuel tanks, one tank for gaseous fuel and one tank for liquid fuel, may not be suitable in a vehicle due to space constraints. A preferable system may be one that stores liquid fuel and pressurized gaseous fuel together in the same fuel tank. In particular, CNG is substantially soluble in gasoline or diesel fuel when stored together at a relatively low pressure (˜100 psi).
The inventors herein have recognized potential issues with the above approach. Namely, fuel metering accuracy may be decreased because liquid fuel supplied from the fuel tank may contain a mixture of liquid fuel and solubilized gaseous fuel, and the gaseous fuel may form bubbles during fuel injection. Furthermore, formation of gaseous fuel bubbles may adversely change the dispersion of injected fuel in the engine, reducing fuel economy and engine efficiency.
One approach which at least partially addresses the above issues comprises a method for an engine, comprising on board a vehicle, supplying fuel from a fuel tank to a fuel separator, wherein the fuel comprises a gaseous fuel solubilized in a liquid fuel, desolubilizing the gaseous fuel from the liquid fuel in the fuel separator, and separating the gaseous fuel from the liquid fuel in the fuel separator.
In another embodiment, a method may comprise on board a vehicle, storing fuel in a fuel tank, wherein the fuel comprises a gaseous fuel solubilized in a liquid fuel, during a first condition, desolubilizing and separating the gaseous fuel from the liquid fuel in a fuel separator, and supplying the gaseous fuel and the liquid fuel to fuel injectors, and during a second condition, supplying fuel from the fuel tank to the fuel injectors while bypassing the fuel separator.
In another embodiment, a fuel system may comprise a fuel tank on board a vehicle, the fuel tank including a gaseous fuel dissolved in a liquid fuel, a fuel injection system downstream from the fuel tank, the fuel injection system including gaseous fuel injectors and liquid fuel injectors, and a fuel separator fluidly coupled between the fuel tank and the fuel injection system.
In this way, the technical result may be achieved in that a consistent dispersion of injected fuel in engine cylinders can be maintained while providing more robust and accurate fuel injection control so that engine emissions may be reduced and fuel economy and engine efficiency may be increased. The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.